1. Field of the Invention
The present invention relates to a technique used for a damper spring device in a transmission unit for transmitting engine power to a transmission in, for example, an automobile. Further, the present invention relates to a flywheel comprising the damper spring device. Moreover, the present invention relates to a clutch disk comprising the damper spring device. Furthermore, the present invention relates to a clutch disk for lockup mechanism comprising the damper spring device.
2. Description of the Related Art
Conventionally, in a manual automobile, rotation of the crankshaft of an engine is transmitted to a transmission as a clutch disk on an end portion of an input shaft of the transmission is pressed against a flywheel on an end portion of the crankshaft by a pressure plate.
However, a sudden torque change may occur depending on the operating state of the engine. In this case, the flywheel and clutch disk are connected so that the torque change is transmitted to the transmission.
If the sudden torque change is transmitted to the transmission, it causes various types of gears in the transmission to produce rattling noise. To overcome this, the clutch disk is provided with, for example, damper spring devices that can absorb the sudden torque change.
Specifically, the clutch disk comprises, for example, two disks. One of the disks is connected to the shaft of the transmission. The other disk is supported on the one disk so as to be rotatable around the crankshaft and the rotary shaft of the transmission. The other disk is supported for rotation relative to the one disk and releasably pressed against the flywheel. The damper spring device is disposed between the one and other disks and elastically supports the rotational displacement of the one disk relative to the other disk.
In the clutch disk constructed in this manner, if a sudden torque change occurs when the other disk is pressed against the flywheel, the other disk is rotationally displaced relative to the one disk, and this rotational displacement is absorbed by the damper spring device. In this way, a sudden torque change of the engine can be absorbed.
An example of the damper spring device used in this manner comprises, for example, an arcuate coil spring, and this coil spring has two types of turns of different diameters, large and small. According to the damper spring device of this type, relative rotation of the other disk is stopped as the turns of a coil strand are brought into fully close contact with one another, and impact attributable to the sudden torque change is absorbed by friction between the turns of the fully compacted strand with the large and small diameters (e.g., Jpn. PCT National Publication No. 2002-507707).
Further proposed is a structure that comprises two types of spring mechanisms configured to absorb impact. These two types of spring mechanisms sequentially operate depending on the magnitude of the impact (e.g., Jpn. Pat. Appln. KOKOKU Publication No. 2-9208). In the structure of this type, the two types of spring mechanisms have two-phase load characteristics.
However, the structure disclosed in Jpn. PCT National Publication No. 2002-507707 is a structure in which the large- and small-diameter turns contact one another and produce friction as they slide radially inward and outward relative to one another, thereby attenuating the impact. Therefore, the spring may be broken by bending stress in a direction such that the coil is spread.
Further, the structure disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 2-9208, which comprises the two types of spring mechanisms, is complicated. According to Jpn. PCT National Publication No. 2002-507707 and Jpn. Pat, Appln. KOKOKU Publication No. 2-9208, furthermore, surging may occur as the impact attributable to the torque change is absorbed, and this surging may be influential.
On the other hand, a buffer is proposed in which two types of coil springs are arranged in series. In this buffer, the two types of coil springs are arranged in series so that an input load can be absorbed as one of the coil springs is contracted. Then, a heavier load can be absorbed as the other coil spring is contracted (e.g., Jpn. UM Appln. KOKOKU Publication No. 34-13828).
Thus, the buffer described above can obtain two-phase load characteristics by means of the relatively simple structure in which the two types of coil springs are arranged in series.
Also in the buffer disclosed in Jpn. UM Appln. KOKOKU Publication No. 34-3828, however, the coil spring may be damaged (e.g., broken) by friction between the turns of the coil spring. Further, surging may occur as the torque change is absorbed, and this surging may be influential.